Field of the Invention
The present invention relates to a semiconductor device package fabrication method, and more particularly to an external terminal fabrication method for a semiconductor device package. Although the present invention has a wide range of applications, it is particularly suitable for a ball grid array (BGA) package.
Discussion of the Related Art
In a conventional BGA package, as shown in FIG. 1, there are provided a plurality of inner leads 2 formed of copper that pass through a substrate 1 to connect the upper and lower surfaces of the substrate 1. A plurality of bonding fingers 2a are formed at respective upper portions of the inner leads 2. A die paddle 3 is mounted on the surface of substrate 1. A semiconductor chip 4 is attached on paddle 3 using an adhesive 5. The bonding fingers 2a of inner leads 2 are respectively connected to bonding pads on the chip 4 by metal wires 6. Molding unit 7 surrounds the chip 4 and metal wires 6 and covers a certain area on substrate 1 by using an epoxy compound. A plurality of solder balls 8 are attached to the respective copper islands 10 formed on respective lower ends of inner leads 2 at the lower surface of substrate 1 and electrically connected to the chip 4 via the respective inner leads 2 passing through substrate 1.
The conventional BGA package is manufactured by the following steps.
First, a plurality of via holes are formed in a substrate by patterning a thin printed circuit board (PCB) and by punching the patterned portions to fabricate a package substrate. A plurality of PCBs with the via holes formed therethrough are stacked and then the substrate 1 having inner leads 2 therethrough is formed by filling Cu metal into the respective via holes to connect the upper and lower surfaces of substrate 1.
Next, the die paddle 3 on which the adhesive pad 5 is glued is mounted on substrate 1 having inner leads 2 therethrough, and a die bonding is carried out for attaching chip 4 onto adhesive 5. A wire bonding is carried out using metal wires 6 to connect respective bonding pads (not shown) formed on chip 4 with respective bonding fingers 2a formed at respective upper ends of inner leads 2. To protect chip 4 and wires 6 from external damage, a molding unit 7 is formed thereover using an epoxy molding compound.
For better adhesion of copper islands 10 and solder balls 8 provided at the lower surface of substrate 1, a flux step is carried out for spreading solder cream on substrate 1.
The position between substrate 1 and a ball mounting device (not shown) is adjusted and solder balls 8 are mounted accordingly. After mounting solder balls 8, solder residue is removed, a reflow step is carried out for leveling the balls, and the surface of the substrate is cleaned using alcohol, acetone or the like to thereby complete the BGA package manufacture.
However, in the conventional BGA package fabrication method, during the ball mounting step for attaching solder balls 8 on the lower surface of substrate 1, it is difficult to align or match the positions between the substrate and the ball mounting device (not shown). Thus, the solder balls are not accurately mounted on desired positions for the copper islands 10 which are on respective lower ends of inner leads 2. Accordingly, a connection fault may occur between inner leads 2 and solder balls (outer leads) 8, or a poor adhesion may result between solder balls 8 and inner leads 2 after ball mounting, thereby resulting in the solder balls becoming detached from the outer leads. Also, an expensive ball mounting device is required which increases the production cost.
Moreover, since a standard diameter for solder balls is 0.76 mm, there is a limit to minimizing the size of the solder balls, and its application has been more difficult in the case of a high density multi-pin structured semiconductor package.